/Engine/Source/Runtime/Core/Public/Internationalization/TextLocalizationManager.h
Get a list of culture names that we have localized resource data for (ELocalizationLoadFlags controls which resources should be checked).
[TArray](API\Runtime\Core\Containers\TArray)< [FString](API\Runtime\Core\Containers\FString) > GetLocalizedCultureNames ( const ELocalizationLoadFlags InLoadFlags ) const